The present invention relates to a micro-lens array sheet which is useful for wide screen display apparatus of the rear projection type television.
In prior arts, there are two types of screens for a LCD rear projection type television. One is a single-sided lenticular screen. The other is a double sided lenticular screen covered with black stripe coatings. They will be explained in detail hereinafter.
An example of the single-sided lenticular screen is explained.
FIG. 11a is a plan view showing the rear projection type display apparatus. A light with a field angle is projected from a projection lens 1 to a Fresnel lens sheet 2 where the light is converted into a parallel beam light. Then, the parallel beam light diffuses in the single-sided lenticular sheet 3, and it passes through the tint layer 6, so that the light 4 with a certain field angle forms an image in the viewer""s eyes.
FIG. 11b is a perspective view showing the single-sided lenticular sheet 3, and FIG. 11c is a section of the single-sided lenticular sheet 3.
In the conventional single-sided lenticular sheet, the convex (or semi-cylindrical) lenses are formed in the vertical direction with respect to viewer""s eye, as shown in FIG. 11b. The inside of the single-sided lenticular sheet is a plastic layer mixed with the light diffusive agent. The parallel incident light is launched into the convex lens, where the light is changed its direction and diffused by the light diffusive agent, so that the image is projected as the image emitting light with a certain field angle.
Here the convex lens is control the horizontal field angle, and the vertical field angle is depend on the light diffusion control of the light diffusive agent.
FIG. 12a is a plan view showing the double-sided lenticular screen covered with black stripe coatings. A light field angle is projected from the projection lens 10 to the Fresnel lens sheet 11 where the light is converted into the parallel beam light, then it is launched into the double-sided lenticular sheet 12. The light diffuses in the double-sided lenticular sheet 12, so that the light 14 with a certain field angle forms an image in the viewer""s eyes.
FIG. 12b is a perspective view showing the double-sided lenticular sheet 12, and FIG. 12c is a section showing the double-sided lenticular sheet 12. The black stripe coatings (light shielding film) 13 enhance the contrast of the image by depressing the reflection of the extraneous light.
The double-sided lenticular sheet 12 has convex lenses on both sides, as shown in FIGS. 12b and 12c. The lenticular elements on the light incident side are shaped in stripes elongating in the direction vertical to the viewer""s eyes. While the light emitting side of the sheet is covered with block stripe coatings (light shielding films).
As shown in FIG. 12c, the conventional micro-lens array sheet has a transparent plastic layer, a plastic layer 18 filled with light diffusive agent, and black stripe coatings (light shielding film) 13. The parallel beam light 16 is launched into the convex lens portion as the incident light, and then it makes a focus inside the lenticular sheet. Then the light diffuses in the plastic layer 18 filled with the light diffusive agent on the light transmitting side of the convex lens.
Here, the convex lens on the incident side is bigger than that of the light emitting side. This is for achieving a function not to deteriorate the light efficiency, in coping with the black stripe coatings (light shielding film) 13 for depressing the extraneous light reflection to the light emitting side. Further, the convex lens on both sides function to control the horizontal field angle, while the vertical field angle depends on the plastic layer 18 filled with the light diffusive agent.
As described above, both conventional single-sided lenticular screen and the double-sided lenticular screen covered with black stripes have strip-shaped lenses each elongating in the direction vertical to the viewer""s eyes. The strip-shaped lenses control the horizontal field angle, but do not control the vertical field angle. Therefore, the vertical field angle is controlled by only the light diffusive agent. Thus, the vertical field angle is not sufficiently wide, which is undesirable. Further, both the horizontal and the vertical field angles are limited to the patterns only symmetrical in the vertical and the horizontal directions with respect to perpendiculars to the surface of the screen.
In addition, a typical problem of the conventional single-sided lenticular screen is that a tint-layer formed in the screen for depressing extraneous light reflection deteriorates the light efficiency of the emitting light to the incident light.
It is, therefore, an object of the present invention to provide a micro-lens array sheet having a wide field angle, a field angle control, a high light efficiency, a high brightness, and a high contrast. Another object of the present invention is to provide a projection type display apparatus provided with such a micro-lens array sheet.
For achieving the above objects, the micro-lens array sheet according to the present invention has a construction as follows.
According to a first aspect of the present invention, a micro-lens array sheet is provided with an array of micro-lenses each shaped in a centro-symmetry convex or concave and a layer of either a light diffusion sheet or a sheet filled with light diffusive agent which is attached on a light emitting side of the micro-lens array sheet, the micro-lenses are aligned in a diamond grid array.
According to a second aspect of the present invention, the micro-lenses are aligned in a grid of a combination of diamond blocks and hexagonal blocks.
According to a third aspect of the present invention, the cycle of the arrangement of the micro-lenses are different in the horizontal direction and in the vertical direction.
According to a fourth aspect of the present invention, the centers of the centro-symmetry micro-lenses are shifted.
According to the above aspect of the present invention, it is able to achieve a wide field angle, a control of the field angle, i.e., asymmetrical controls of the vertical and the horizontal field angles and a high brightness. Further, the micro-lens array sheet according to the present invention is able to achieve the high light efficiency and the high contrast by the courtesy of forming a light shielding film which does not depress the light transmittancy of the light emitting side of the sheet.
Additional objects and advantages of the present invention will be apparent to persons skilled in the art from a study of the following description and the accompanying drawings, which are hereby incorporated in and constitute a part of this specification.